troubleshooting with oil leak

I would clean it up really well and drive it once. Then come home and inspect for a snail trail of oil.

Good luck.

Like JT said, the best way to figure it out is to clean it up, and then take it for a spirited drive, then let it idle a few minutes, then shut it off and check right away for oil splatter. You should be able to narrow down the general area the oil (if it's oil) is coming from, and by letting it idle a few minutes, you'll allow any excess to drip.. giving you yet another clue as to where you need to look.

I doubt it's an oil pan leak, unless you've recently been messing with it or something. My money is on a rear main seal leak.

If its all over the tranny Id bet that its coming from the rear lower intake seal. Its actually pretty common in mustangs. I did mine about a year ago and the valve seals in the heads and now I dont burn any noticeable amount of oil and theres no longer an inch of goop on my bellhousing. look down where the PCV is and if theres oil around there its more than likely your rear intake seal.